Shark population expected to nosedive in 2100

By the year 2100, shark populations could undergo steep declines — by up to 44 percent — and remaining sharks may lose much of their ability to sense the odor of food, predict two new studies.

The first experimental investigation on the effects of climate change and ocean acidification on sharks is published in the journal Proceedings of the Royal Society B.

“With this study we show, for the first time, that cartilaginous fishes (sharks and rays) may face similar biological impairments with high carbon dioxide and warming as those observed previously for bony fishes,” lead author Rui Rosa told Discovery News.

“Besides habitat degradation and overfishing, ocean acidification also directly affects shark fitness and survival,” added Rosa, a senior research fellow and the University of Lisbon’s Center for Oceanography.

For the study, Rosa and his team incubated 60 shark embryos at the Tropical Marine Center in the U.K. The embryos previously were collected from waters around Lungsod Ng Cebu, in the Philippines. Some of the embryos were exposed to the slightly higher temperatures and lower pH levels predicted by the year 2100.

Lower pH levels are expected due to carbon dioxide release into the atmosphere. Human sources of CO2 result from burning of fossil fuels, such as coal, oil and natural gas, as well as from activities like deforestation and cement production. Once released, the CO2 can dissolve into oceans where it may reduce pH, causing acidic waters.

Thirty days after the shark embryos hatched, survival rapidly declined by up to 44 percent for those exposed to the warming and acidification conditions that are expected by 2100. Those that did survive “became more lethargic,” Rosa said.

He and his team predict that tropical sharks may be more vulnerable to the expected changes “because they have evolved in a relatively more stable environment,” he explained. Such sharks include the bamboo shark, zebra shark, scalloped hammerhead shark, whitetip reef shark, whale shark, great hammerhead shark, nurse shark, tiger shark, bull shark and many more.

A second study, published in the journal Global Change Biology, also exposed sharks to the lower pH levels predicted by the year 2100. This time, however, the researchers focused on how the predicted change will affect sharks’ ability to sense the odor of food.

Sharks can find prey using other senses, such as hearing and their ability to detect electrical impulses, but chemical sensing — akin to our ability to smell — is critical to shark hunting success.

“The sharks’ tracking behavior and attacking behavior were significantly reduced,” said lead author Danielle Dixson, who is an assistant professor in the School of Biology at the Georgia Institute of Technology.

“Sharks are like swimming noses,” she added, “so chemical cues are really important for them in terms of finding food.”

Sharks have had to deal with temperature and ocean acidification changes in the past, but the current and predicted changes are unprecedented.

“It’s the rate of change that’s happening that’s concerning,” Dixson concluded. “Sharks have never had to deal with it this fast.”

Jennifer Viegas, Discovery News, 9 September 2014. Article.

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